Conventionally, there is well-known a damper provided with blade portions extending in a spiral manner in the first rotor portion (see paragraph [0014] and FIG. 4 of Patent Document 1).
When the aforementioned conventional first rotor portion is rotated in one rotational direction, for example, clockwise, end portions of the blade portions separate from an inner circumferential surface of the housing so as to become a low torque (see paragraphs [0020] and [0021], and FIGS. 4 and 7 of the Patent Document 1).
On the other hand, when the aforementioned conventional first rotor portion is rotated in the other rotational direction, for example, counterclockwise, the end portions of the blade portions abut against the inner circumferential surface of the housing, and a silicon oil only flows along an orifice so as to become a high torque (see paragraphs [0022] and [0023], and FIGS. 4 and 7 of the Patent Document 1).
Also, conventionally, there is well-known a damper provided with plural intervening blade portions extending in a radial manner in the rotor portion, and forming a constricted portion on a base portion side of the blade portions so as to narrow a width. Accordingly, the damper facilitates an elastic deformation of the blade portions in response to a resistance received from the viscous fluid, and also changes a clearance in a position wherein a circular surface of the blade portions and an inner circumferential wall of the housing come the most close (see paragraphs [0030] and [0046], and FIGS. 1 and 6 of the Patent Document 1).